(Department of Geology and Environment of Ministry of Land and Resources)
1 overview
Inside the earth is a huge heat source reservoir, which contains huge heat energy. Shallow geothermal energy is an important part of the earth's thermal energy, which usually refers to low-temperature geothermal resources hidden in rocks (soil) in the shallow crust under the surface thermocline, and its thermal energy mainly comes from heat conduction in the deep earth. The temperature of shallow geothermal energy is slightly higher than the local average temperature by 3 ~ 5℃, which is relatively stable, widely distributed and convenient for development and utilization. It has a very broad development and utilization prospect. The utilization of shallow geothermal energy is mainly through the heat exchange mode of heat pump technology, transforming the low-level heat source existing in the stratum into the available high-level heat source, which can provide both heating and cooling. At present, the depth of economic development and utilization of shallow geothermal energy is generally less than 200m m.
The continuous improvement and wide application of heat pump technology provide conditions for the development and utilization of shallow geothermal energy. The heat pump system used for the development and utilization of shallow geothermal energy, collectively referred to as "ground source heat pump system", is a heating and air conditioning system which takes rock and soil, groundwater (or surface water) as low-temperature heat sources and consists of a water source heat pump unit, a geothermal energy exchange system and a building system. It is an energy-saving and environment-friendly air conditioning system. According to the different forms of geothermal energy exchange, ground source heat pump systems are divided into ground source heat pump systems, underground water source heat pump systems and surface water source heat pump systems.
Ground source heat pump technology is an efficient and energy-saving air conditioning technology that uses shallow geothermal energy to take heat for heating and cold for refrigeration. Its working principle is to use the relatively stable room temperature of underground soil or groundwater, input a small amount of high-grade electric energy, and use the pipeline system buried around the building or groundwater to exchange heat with the inside of the building to realize the transfer of low-grade heat energy to high-grade air conditioning system. It consists of water circulation system, heat exchanger, ground source heat pump unit and control system. In winter, boilers are replaced by soil heat, buildings are heated by hot air at about 30 ~ 40℃, ordinary air conditioners are replaced by soil heat in summer, and buildings are cooled by cold air at about 10 ~ 17℃. At the same time, it can also supply domestic hot water.
A large number of examples at home and abroad show that the use of ground source heat pump system to develop and utilize shallow geothermal energy for building heating and air conditioning has the characteristics of convenient access, no pollution and low operating cost. Shallow geothermal energy is an ideal "green energy" and heat pump technology is a "green technology". Its main features are:
(1) Sustainable utilization of resources. Shallow geothermal energy storage is like a huge thermal energy storage device, which uses heat pump system to heat and air-condition buildings, takes heat from the ground in winter to heat buildings, and absorbs heat from buildings in summer and releases it to the ground for storage. In this way, the heat required for building heating in winter can be generally balanced with the heat in the deep part of the earth and the heat stored in summer, so that the shallow geothermal energy can be continuously utilized.
(2) High efficiency and energy saving. Because the shallow ground temperature is slightly higher than the local average temperature and relatively constant, and the temperature is higher than the ambient temperature during heating in winter, the circulating evaporation temperature of heat pump increases and the energy efficiency ratio increases; When cooling in summer, the temperature is lower than the ambient temperature, which improves the cooling effect and unit efficiency. The refrigeration and heating coefficient of ground source heat pump can reach above 4.0. It is about 40% higher than the traditional air source heat pump, and its operating cost is only 50% ~ 60% of that of ordinary central air conditioning. Compared with electric boiler and electrothermal film heating, it can save about 70% electric energy.
(3) No environmental pollution. When the ground source heat pump is running, except for a small amount of electric energy, it only needs circulating water or other liquids that exchange heat with underground rock and soil layers (including water in rocks, soil layers and cracks), which basically consumes no water, discharges no waste and does not cause any pollution to the surrounding environment.
(4) Low operating cost. Less maintenance, high degree of automation, operating costs are generally only equivalent to 30% ~ 70% of the cost of ordinary heating and air conditioning.
(5) One machine is multi-purpose. A ground source heat pump can provide heating, cooling and domestic hot water, which can replace the original boiler and air conditioning system, and the one-time investment is reduced.
(6) Saving land resources. Ground source heat pump has no other installation equipment except main engine and circulating water pump. Compared with boiler room, it saves water treatment room, fan room, chimney, coal yard and muck yard, and saves land resources.
(7) Flexible operation, stability and reliability, long service life: each unit can run independently, and the failure of individual units will not affect the operation of the whole system. The operating condition of the unit is stable, not affected by the change of ambient temperature, and there is no need to defrost in winter. The heat pump has few moving parts, basically no maintenance, stable and reliable operation, and its service life can reach 20 years.
(8) High degree of automation: The ground source heat pump is generally controlled by computer, and the number of compressor workstations can be adjusted according to the change of external load, and various protection measures such as compressor over-temperature protection and water cut-off protection can be provided, so that unattended operation can be realized.
(9) Wide application range: it can be applied from cold regions to tropical regions.
(10) is easy to manage. It can realize the independent meter charging of the unit and facilitate the management of the whole system.
The application of ground source heat pump system is restricted by local hydrogeological conditions. The hydrogeological conditions in this area determine the possibility and utilization mode of using ground source heat pump for heating and air conditioning. Generally speaking, in areas with shallow groundwater level, thick aquifer, strong permeability and easy recharge, it is suitable to use ground source heat pump with groundwater as the carrier; Vertical ground source heat pump is suitable for sandy soil distribution areas with shallow groundwater level, thick loose layer, poor permeability and difficult recharge. Ground source heat pump is not suitable for rock areas with deep groundwater level, small thickness of loose layer, weak permeability of rock and soil layer and no groundwater exploitation.
2 international ground source heat pump technology and the development trend of shallow geothermal energy application
The concept of "heat pump" was put forward by Swiss in 19 12, and the first heat pump system was born in 1946 in Oregon, USA. From 65438 to 0974, the governments of Switzerland, the Netherlands and Sweden gradually funded the establishment of demonstration projects. In the late 1980s, heat pump technology became more and more mature. In the past 10 years, the average growth rate of heat pumps in about 30 countries reached 10%, which was widely recognized by the international community for its reduction of carbon dioxide.
At present, the countries that use heat pump technology to develop and utilize shallow geothermal energy include the United States, Northern Europe, Sweden, Switzerland and Germany, Canada, Austria, France and the Netherlands, and China, Japan, Russia, Britain, Norway, Denmark, Ireland, Australia, Poland, Romania, Turkey, South Korea, Italy, Argentina, Chile and Iran.
The rapid growth of heat pumps is mainly in the United States and Europe. At present, the global installed capacity may be close to 10 100MWt, the annual energy utilization is about 59,000 TJ (16470 GWh), and the actual installed capacity is about 900,000 units. According to incomplete statistics, the countries with the largest installed capacity of ground source heat pumps are the United States, Sweden, Germany, Switzerland, Canada and Australia (see
Table 1 Countries with the largest installed capacity of ground source heat pumps
In the United States, nearly 50,000 to 60,000 heat pump units are installed every year, and more than 600 schools have installed heat pump systems for heating and cooling. In Switzerland, due to the plateau climate and insufficient sunshine in winter, the water source heat pump system grows rapidly at the rate of 15% per year. At present, there are more than 250,000 heat pump systems in operation in Switzerland, which is the country with the largest heat pump density in the world. In Britain, although the geological conditions are very complicated. But heat pump technology has also developed from a very small beginning to the whole of Britain. The fields involved are: private buildings, real estate development, public facilities, etc. At present, the installation of ground-source heat pumps in Sweden accounts for 60% of the total demand load, especially after entering 2 1 century, the installation of heat pumps in Sweden has increased more rapidly, and the sales of heat pumps in 200 1 year alone exceeded 25,000. Although most of Australia is located in the tropics, the number of imported heat pumps has reached more than 23,000.
Ground source heat pumps are widely used in Japan, South Korea, the United States, Central Europe and Northern Europe. According to 1999 statistics, the proportion of ground source heat pump in residential heating devices is 96% in Switzerland, 38% in Austria and 27% in Denmark. The ground source heat pump system in the United States accounts for 30% of the new buildings in 1998, and it is growing steadily at the rate of 10%. The most famous ground source heat pump project is the waterfront office building in Louisville, Kentucky, with a service area of 15.8× 104 m2, saving 25,000 USD per month. With the application and development of this technology, the research on its organization has also developed rapidly. According to relevant data, the high-temperature water-ground source heat pump developed in Japan has an outlet water temperature of 80 ~ 150℃ and a heating coefficient of COP as high as 8.0.
Due to the maturity of ground source heat pump technology, the extensive utilization of shallow geothermal energy has been effectively promoted. In recent years, the scale and speed of shallow geothermal energy development and utilization in various countries are increasing rapidly. From the development trend of foreign countries, the development and utilization of shallow geothermal energy (low temperature energy contained in shallow rock and soil) will be the mainstream and direction of geothermal resources development and utilization.
3 China shallow geothermal energy development and utilization status
The research on heat pump in China began in 1950s. Professor Lv Canren from the Institute of Thermal Energy of Tianjin University carried out the research on heat pumps in China in 1954, and successfully developed the first water-cooled heat pump unit in China in 1965. However, due to various reasons, the development was slow, and it was not until the late 1980s and early 1990s that a new round of research in related fields began. Since the beginning of 2 1 century, China has made a number of remarkable achievements in heat pump model simulation, test equipment, energy consumption evaluation and system materials research. With the shortage of traditional energy, people's attention to the development of new and renewable energy and the maturity of heat pump technology, the development and utilization of heat pump technology and shallow low-grade geothermal energy have developed rapidly.
Our government attaches great importance to the development and utilization of heat pump technology and shallow geothermal energy. 1994 in March, the State Council approved the sustainable energy plan under the agenda of China 2 1 century. 1997 1 1 The former State Science and Technology Commission and the US Department of Energy signed the Cooperation Agreement on Geothermal Energy Production and Application in Beijing, and the Chinese and American governments began to carry out technical cooperation in the field of renewable energy. 1998165438+10, the Work Plan of Sino-US Government Cooperation in Promoting American Ground Source Heat Pump Technology was implemented, and Beijing Jike Ground Source Heat Pump Technology Co., Ltd., Shanghai Dingda Energy Co., Ltd. and Guangzhou Xinlida Co., Ltd. were determined as the executing units of the Sino-US government ground source heat pump cooperation project. According to this plan, three demonstration projects, Beijing Jiaheyuan International Apartment, Ningbo Garment Factory and Guangzhou Song Tian College Teaching Building, were officially launched on 132380㎡, with a total construction area of 132380㎡, of which Beijing Jiaheyuan International Apartment is the largest, reaching 88,000 ㎡. In June 2000, China's Ministry of Science and Technology hosted the "American Ground-to-Air Ground Source Heat Pump Technology Exchange Conference" in Beijing, which further promoted the application of heat pump technology. According to statistics, by the end of 2003, Beijing Jike Company alone had built a billion-dollar rustic project.
Beijing is one of the earliest and fastest developing areas in China to use ground source heat pump technology to develop shallow geothermal energy for building heating and air conditioning. In recent years, the number of projects using shallow geothermal energy to heat and air-condition buildings has increased rapidly. By the end of 2004, there were more than 200 units in Beijing with a total construction area of 4.2 million square meters, which used shallow geothermal energy for heating or cooling. Its architectural types include ordinary houses, office buildings, high-class hotels, schools, kindergartens, shopping malls, hospitals, nursing homes, archives, stadiums, factories, sewage stations, landscape pools and so on. Among them, the largest single project construction area of groundwater ground source heat pump system is 6.5438+0.8 million m2, and the largest single project construction area of ground source heat pump system (also known as ground source heat pump system) reaches 6.5438+0.3 million m2. At present, UFIDA Software Park, a single project of ground-source heat pump system under implementation by Huaqing Geothermal Group, will have a heating and air-conditioning area of 200,000 square meters. Several representative ground source heat pump heating and air conditioning projects are shown in Table 2.
Table 2 Brief introduction of representative ground source heat pump heating and air conditioning projects in Beijing
Tianjin is also one of the earliest areas in China where ground source heat pump system is used for heating and air conditioning. In recent years, the heating and air conditioning projects of ground source heat pump systems, such as Shibajie Haibin Avenue Development Company in Tianjin Development Zone, Tianjin Geology and Minerals Jewelry Company and Guwen Street in Haihe Business District in downtown Tianjin, have been established one after another. It is developing rapidly at present.
Henan, Inner Mongolia, Shandong, Guangdong, Anhui and other places have also begun to explore and pilot the development and utilization of shallow geothermal energy. With the adjustment of China's energy structure policy, the traditional methods of boiler heating and air source heat pump cooling mainly based on coal and electricity will be replaced by more efficient methods of ground source heat pump heating (or cooling) with shallow geothermal energy as heat source (or cooling). With the gradual improvement of ground source heat pump technology, shallow geothermal energy will surely become the most common and main energy source in the development and utilization of geothermal energy in China in the future. In building heating (or cooling) in China, the proportion of shallow geothermal energy will be higher and higher.
4 main problems
Although the ground source heat pump technology and its exploitation and utilization of shallow geothermal energy have achieved remarkable results in China, due to its short development time, it is still in its infancy, the regional development is very uneven, and some existing problems are increasingly apparent, which need us to seriously study and solve, otherwise it will directly affect the scientific development and sustainable utilization of shallow geothermal energy resources. The main questions are:
(1) The degree of social cognition is low. At present, the social understanding of shallow geothermal energy resources is still very low. People don't know much about the rich shallow geothermal energy resources, their characteristics and heat pump technology, and even a considerable number of professional design units lack understanding of this, which directly affects the wide application of shallow geothermal energy.
(2) The development technology level is not high. The series of ground source heat pump products which are suitable for China's characteristics and meet different requirements have not yet been formed and need to be actively developed; The professional designers of ground source heat pump heating and air conditioning engineering are generally lacking, and the problems of mismatched and conservative system design are more prominent. The theory of heat transfer calculation of soil buried pipe is immature, lacking design standards, and the engineering quality is difficult to guarantee, which limits its wide application.
(3) The development and utilization projects are out of touch with the resource exploration and evaluation, and there is a certain blindness. Hydrogeological conditions determine the way and scale of exploitation and utilization of shallow geothermal energy. However, at present, the development of shallow geothermal energy is mostly out of line with exploration and evaluation, and some development and utilization schemes have no scientific basis, and the development scale does not match the resource conditions, which leads to blindness, resulting in low engineering benefits and low success rate. Therefore, the development and utilization of shallow geothermal energy must be based on hydrogeological exploration and evaluation, and the feasibility, suitability and development and utilization ability of shallow geothermal energy should be evaluated, and the development and utilization scheme and the type of heat pump system (ground source heat pump or underground water source heat pump, etc.) should be formulated according to local conditions. ) should be selected, and determine the scientific data such as buried depth and density.
For the projects and areas that have developed and utilized shallow geothermal energy, most of them have not monitored the temperature of rock and soil, the temperature of groundwater and its water quality in the environmental geological bodies within their influence, nor have they timely analyzed the changing law of geothermal energy field and conducted environmental impact assessment, let alone cared about the future changing trend.
(4) The technical standards and specifications of shallow geothermal energy development and utilization lag behind. At present, there is a lack of technical specifications such as shallow geothermal energy exploration and evaluation and shallow geothermal energy environmental impact assessment, which makes the exploration and evaluation work lack standards and methods are not unified. Engineering design lacks systematic design specifications, and most of them are in a state of no standards to follow. Lack of qualification management of development units and necessary demonstration procedures for projects implemented. Shallow geothermal heating (or cooling) is a systematic project. The above-ground HVAC system, the exploration and evaluation of underground resources, the design and construction of well location and buried pipe system are an organic whole, and all disciplines must design and construct in a unified way and work together. Otherwise, the shallow geothermal energy heating (or cooling) project will cause the adverse consequences of mismatched or poorly matched heat pump systems and low success rate.
(5) The research and development of related technologies is lagging behind. Due to the short development and utilization time of shallow geothermal energy in China, some supporting technical measures and testing equipment can not keep up. For example, the research and development of deep geotechnical thermophysical properties testing technology and instruments, the simulation test research of underground heat transfer models in different regions, the heat transfer enhancement of underground heat exchangers, the development of system design software, the research of ground source heat pump simulation and optimal matching parameters, and the research of high-performance backfill materials are all urgently needed.
(6) Lack of necessary support and incentive policies. Shallow geothermal energy resources have great potential for development and utilization, and are renewable and pollution-free, which is irreplaceable by any fossil fuel. However, the initial one-time investment is also large. To achieve economies of scale, governments at all levels need to give support in fiscal and taxation policies, otherwise the comprehensive promotion and application will be limited. As far as the whole country is concerned, at present, only Beijing has issued an incentive policy, and the municipal finance will subsidize those who use heat pump technology for heating (cooling) according to the benefit construction area. However, in some areas, instead of encouraging policies, restrictive policies have been introduced. For example, not only the underground source water is charged, but also the source water reinjected into the ground is charged again, which increases the burden on enterprises and makes the energy-saving and environmental protection effect of shallow geothermal energy not reflected in the economic benefits, thus greatly limiting the utilization and development of heat pump technology and shallow geothermal energy.
5 countermeasures
The exploitation and utilization of shallow geothermal energy has gradually arisen and developed rapidly in China. In recent years, its development speed in heating (air conditioning) has exceeded the traditional geothermal resources. With the improvement of people's understanding and the launch of demonstration projects, its development and utilization will attract more people's attention, and more and more building heating and air conditioning projects will use shallow geothermal energy resources. In order to promote the rational development and utilization of shallow geothermal energy resources, the following countermeasures must be taken.
(1) Actively carry out exploration and evaluation of shallow geothermal energy resources, and formulate the overall development plan for development and utilization. It is an indisputable fact that shallow geothermal energy resources are widely distributed on the earth's surface and have broad utilization prospects. However, the way of development, the amount of possible utilization and the degree of impact on the environment after long-term utilization are all limited by local specific hydrogeological conditions (groundwater burial conditions, stratum structure, aquifer permeability, groundwater quality, etc.). ). Only by understanding these conditions can we make a correct choice for the utilization of shallow geothermal energy. As far as a region is concerned, we can make a reasonable judgment on the areas suitable for the development and utilization of shallow geothermal energy, lots with different utilization methods, possible utilization scale and potential environmental geological problems.
Deploy and carry out exploration and evaluation of regional shallow geothermal energy resources. At present, we should start from the key cities in the plain area and carry out the exploration and evaluation work with the scale accuracy of 1∶65438+ 10,000 as the main body. On the basis of the original hydrogeological exploration results, the necessary exploration work to obtain parameters such as thermal conductivity and permeability coefficient of rock and soil is supplemented. The depth of exploration work is generally controlled at 200m.
On the basis of exploration and evaluation, the development and utilization plan of shallow geothermal energy is compiled, the layout is reasonable, the areas suitable for development and utilization are determined, the lots with different utilization modes (groundwater and buried pipes) are delineated, and the reasonable development and utilization scale, geological disasters and environmental geological problems are put forward.
(2) Promote the construction of demonstration projects and promote the development and utilization of regional shallow geothermal energy resources. There are great differences between north and south in China, and the geological conditions are complex. The successful application of shallow geothermal energy in one area is limited by the specific conditions in this area, and it cannot be completely applied to other areas. Different ways of utilization experience also have their own characteristics and corresponding utilization modes. The popularization and application of shallow geothermal energy in a region should not only absorb general experience, but also, more importantly, establish demonstration projects in line with local conditions, explore methods, sum up experience, popularize and apply, and promote local development and utilization.
(3) Relying on scientific and technological progress and innovation, improve the technical level of shallow geothermal energy application. Shallow geothermal energy utilization involves resources exploration and evaluation, underground heat exchange, heat pump, building heating (cooling) system, automatic control and other supporting technologies. , and involves the application technology of multi-disciplinary correlation and reference, which requires both self-improvement and mutual coordination and cooperation. At present, it is especially necessary to strengthen the underground heat exchange technology, the development of ground source heat pump products suitable for China's characteristics and needs, the serialization and standardization of products, the optimization of system design and the development of related instruments. To improve the overall technical level.
(4) Introduce relevant policies to encourage the development and utilization of shallow geothermal energy resources: the initial investment of shallow geothermal energy development and utilization is high, but the operation and management cost is low, and it is clean, efficient and energy-saving. It is a clean energy with good development prospect and sustainable utilization. The government should issue relevant policies and regulations to support and encourage the development and utilization of shallow geothermal energy resources. Local governments at all levels can refer to the practice of Beijing Municipal Government, give financial subsidies to users of heating (or cooling) according to the built heating (or cooling) building area, support and encourage the popularization and application of heat pump technology, and promote the development and utilization of shallow geothermal energy. It is suggested that the central government arrange some special funds for the development of renewable energy to support and encourage the development and utilization of shallow geothermal energy in the demonstration area.
(5) Formulate relevant technical standards and norms to standardize the development and utilization of shallow geothermal energy resources. From June 5438 to October 2005 10, the Ministry of Construction and the General Administration of Quality Supervision, Inspection and Quarantine jointly issued GB50366-2005 "Technical Specification for Ground Source Heat Pump System", which is suitable for the systematic engineering design, construction and acceptance of heating, air conditioning or heating domestic hot water with rock and soil, groundwater and surface water as low-temperature heat sources and water or aqueous solution containing antifreeze as heat transfer media. Its release and implementation will help unify the design quality of shallow geothermal energy development and utilization projects. At present, it is urgent to formulate and promulgate technical specifications and standards such as shallow geothermal energy exploration and evaluation and shallow geothermal energy geological environment impact assessment. So as to standardize the exploration and evaluation of shallow geothermal energy resources, the design of buried pipe of ground source heat pump and the evaluation of geological environment impact, and improve the development and utilization level of shallow geothermal energy.
(6) Carry out dynamic monitoring of underground heat exchange system of shallow geothermal energy development and utilization demonstration project. In areas where shallow geothermal energy has been developed and utilized, different types of typical areas are selected to carry out dynamic monitoring of underground heat exchange system, and long-term monitoring and research are carried out on the dynamic balance of water and heat in underground sites, so as to accumulate data and provide basis for shallow geothermal energy evaluation, optimal design of underground heat exchange system engineering, improvement of standards and protection of resources and environment.
(7) Establish and improve the database and information system for shallow geothermal energy development and utilization: the underground heat exchange system for shallow geothermal energy development and utilization is a permanent project, and some ground buildings have disappeared, and the underground heat exchange system (buried pipes, water source wells, etc.). ) will stay deep underground for a long time, which will have a potential impact on the local environment and the production and life activities of future generations. In order to strengthen the management and resource protection of shallow geothermal energy development and utilization, the database and information system of underground heat exchange engineering for shallow geothermal energy development and utilization in China and all provinces (autonomous regions and municipalities) should be established as soon as possible.